Name: Glenn M.
I understand why the leaves change color. If chlorophyll
is the same then why does not grass or conifers change color in the autumn.
Deciduous plants lose their leaves by winter; evergreen plants retain their
leaves much longer, but they too, eventually lose their leaves or
needles. There are conifers that do change color early in autumn and lose
their needles by winter.
Anthony R. Brach
Certain trees, for example red maples, have colored substances in the
leaves in addition to chlorophyll. During the spring and summer the color of
these other substances are overwhelmed by the intense green color of
chlorophyll. In the autumn when the chlorophyll is no longer present, these
underlying substances show off their color. Other plants, e.g. most grasses
I can think of, do not have any of these colored substances, so in the autumn
they just turn brown.
It is simply a matter of different adaptations to seasonal changes. Most
conifers have leaves with small surface area and waxy coating to reduce
water loss in winter, which is more of a problem to many plants than
temperature. Lawn grasses and many other plants have natural "antifreeze"
like components in their leaves that keep tissues from being destroyed by
freezing. Interestingly many of our native prairie grasses do turn subtle
but very lovely colors in fall as they enter winter dormancy.
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Update: June 2012